The proposed research will examine the drug-behavior interactions which determine whether a given drug injection will reinforce or suppress behavior which precedes the injection. Since the reinforcement model of drug dependence is becoming more important in drug abuse research, an understanding of the conditions leading to the reinforcing effects of drugs is of value. Rats will be allowed to drink saccharin solution and then injected with one of a variety of doses of several drugs, to include amphetamine, cocaine, morphine, and pentobarbital. Several days later saccharin will again be placed in the rats' drinkin tubes, an the conditioned drug effect on drinking as well as on locomotor activity will be assessed. These conditioned effects will be compared with the effects obtained when drugs are injected prior to the test. The effects of contingent injections will also be studied. These injections will be automatically administered following a specified number of occurrences of one behavior or the other. It is predicted that, under appropriate dosage and suppress drinking behavior. These effects will be compared with the effects of similarly scheduled noncontingent drug injections.